The invention relates to a digital-to-analog converter using switched capacitors to produce a continuous time output.
A general trend in the integrated circuit industry is towards higher integration. Particularly in consumer markets such as portable communications, computer products, etc., higher levels of integration result in a smaller bill of materials, and therefore, power, area and cost savings. The performance parameters of circuits targeted for a highly integrated application specific integrated circuit (ASIC) can be very different from those of a general purpose circuit with the same function. Therefore, the design of such circuits should be approached differently. In the design of general purpose digital-to-analog converters (DACs), switched-capacitor charge redistribution structures have largely been avoided for a variety of reasons, including the need for a clock and the desire to avoid switching noise on the continuous time output of the DAC. Instead, attention has focused more heavily on switched-current or resistive ladder techniques.
In conventional standard mixed signal IC technology, polysilicon capacitors provide the best component matching per unit of area. It makes sense, therefore, to use poly--poly capacitors as the basic unit element in a high resolution converter. Especially in highly integrated mixed signal chips where a clock is readily available, a capacitor based DAC can save area and power over structures which rely on matching currents or voltages in transistors and/or resistors.